In FIG. 1, an exemplary gas turbine 10 is reproduced in a partially sectioned view. The gas turbine 10 from FIG. 1 comprises a rotor, rotatably mounted about a machine axis 18, with a rotor shaft 17 and a blading arrangement which on one side is part of a compressor 11 for the inducted combustion air and on the other side is part of a turbine 14 for expanding the hot gas which is produced. A combustor 13, into which an annular arrangement of burners 12 injects a fuel-air mixture for combustion, is arranged between compressor 11 and turbine 14. The combustor 13 and the adjacent turbine 14 are enclosed by an outer casing 15, onto which an annular exhaust gas housing 16 is flanged.
The exhaust gas housing 16, in relation to the principal axis, comprises a support structure (23 in FIG. 3) and a flow liner (19 in FIGS. 2-4; in FIGS. 2 and 3 only one half of the flow liner is shown in each case), which has to guide the discharging exhaust gases from the turbine 14 in an annular passage so that no flow losses occur as far as possible. In this case, the flow liner 19, as seen aerodynamically, is a part of the exhaust gas diffuser which converts the high flow velocity of the exhaust gas into pressure.
As shown in FIG. 2, the flow liner 19 comprises an annular inner liner 22, radial liner ribs 21 and an annular outer liner 20, which in the majority of applications form a unit, i.e. are welded. Naturally, the halves of the flow liner 19 (top part and bottom part) are separable in a parting plane for service reasons.
As a result of the existing struts 25 of the support structure 23, which serve for connecting an inner ring 26 and an outer ring 24, the flow liner 19 cannot be completely manufactured outside the support structure 23 and then installed. Only the part of the flow liner 19 which is shown in FIGS. 2 and 3 can be prefabricated, this part having corresponding recesses 27 at the points by which it has to be slid over the struts 25 of the support structure 23. This prefabricated part, according to FIG. 3, is then inserted (arrow) into the support structure 23 in the flow direction, and finally, according to FIG. 4, in the regions of the recesses 27 is completed by rearwards insertion and welding of correspondingly designed rear parts 30. The rear parts 30 are provided on their radial ends with fitting flanges 31, 32, on the edges 33, 34 of which the welded seams are run along.
As a result of these welds on the flow liner 19, at least two axial welded seams (35, 26 in FIG. 5) per rib are formed, specifically one each on the outer liner 20 and on the inner liner 22. If provision is made on the side of the liner 20, 22 facing away from the flow for annular reinforcing ribs (37 in FIG. 5), the reinforcing ribs 37 also have two radial welded seams each. With all these welded seams, the required quality is very difficult to achieve because their locations inside the support structure 23 are accessible only with difficulty.
During operation, the flow liner 19, as a result of the high temperatures and the flow velocity of the exhaust gases of the gas turbine, is exposed to severe vibrations and also severe thermal stresses. Moreover, the flow liner 19 has different degrees of rigidity between inner liner 22 and outer liner 20 as well as on the periphery, in the region of the ribs 21, and therebetween. As a result of these loads, cracks develop, the starting points of which—contingent upon notch factors and weakening as a result of welding—in most cases are the welded seams at the outlet of the flow liner 19 (see FIG. 5).